The invention relates to a vehicle brake system, which comprises a motor/pump unit with an electric motor and at least one pump for delivering brake fluid. The electric motor in this case has a stator, in which a rotor is rotatably disposed. The pump is disposed substantially inside the rotor and is drivable by the latter. The invention further relates to such a motor/pump unit.
The motor/pump unit is used to deliver brake fluid to and from wheel brakes of the vehicle brake system in order to actuate and release said wheel brakes. Vehicle brake systems of said type are also known as electrohydraulic brake systems, which may be operated during a so-called antilocking, antispin or vehicle dynamics control operation. The motor/pump unit may be disposed directly adjacent to a wheel brake of a vehicle or may be used as a central supply organ for a plurality of wheel brakes.
From U.S. Pat. No. 4,435,021 A a brake system having a vehicle brake actuator is known, in which an electric motor comprises a stator winding provided in a stationary manner and a rotor provided rotatably therein. The rotor carries a plurality of axial pistons, which are supported against an inclined end face and with the latter form a swash-plate pump. During operation of the swash-plate pump, brake fluid exits at the axial pistons and washes around the rotor. The brake fluid also passes into a gap between stator winding and rotor, gives rise there to a high fluid frictional resistance and reduces the magnetic flux between stator winding and rotor. The electric motor therefore has a low dynamic response, i.e. poor starting and response characteristics.
DE 195 42 654 A1 describes an electronically controllable brake system for motor vehicles comprising a brake pressure transmitter unit and a motor-driven auxiliary pressure source. The auxiliary pressure source, in addition to or instead of the brake pressure transmitter unit, supplies wheel brakes with hydraulic fluid. The brake system further comprises a motor-driven hydraulic pressure source, which boosts an actuation of the brake pressure transmitter unit by means of a brake pedal or which instead of the brake-pedal effects an actuation of the brake pressure transmitter unit. The auxiliary energy source and the hydraulic pressure source are driven by the same motor and are in constant driving connection with the latter. The arrangement of auxiliary energy source, hydraulic pressure source and motor takes up a great deal of installation space.
An object of the invention is to improve a vehicle brake system of the type described above.
An object of the invention is achieved by a vehicle brake system comprising a motor/pump unit, which has the features described above and is developed in such a way that there is disposed adjacent to the motor/pump unit at least one aggregate (i.e., an attached assembly such as a pneumatic or hydraulic pump in addition to the pump of the motor/pump unit), which is drivable with the aid of the rotor.
By virtue of the solution according to the invention the arrangement of motor/pump unit and aggregate is of a particularly compact design and takes up only a little installation space. Because of the compact form of construction only low masses are to be accelerated, with the result that the motor/pump unit and the additional aggregate have good starting and response characteristics. Brake fluid may therefore be delivered in a highly dynamic manner. The electric motor and the pump are themselves of an extremely compact, so-called cartridge style of construction. In this case, it is also possible for a plurality of pumps to be in particular radially surrounded by a rotor.
An object is achieved according to the invention also by such a motor/pump unit.
An advantageous development provides that the rotor is in constant driving connection with the aggregate. This connection may be easily formed e.g. via a shaft, with the result that a costly coupling susceptible to faults is not required.
The aggregate advantageously takes the form of a pneumatic or hydraulic pump. The motor/pump unit together with the aggregate therefore forms a compact supply unit, which provides all of the pressure energies needed for a vehicle brake system.
In an advantageous development, the aggregate is a hydraulic aggregate with a radial piston pump, such as is used in known ABS and ASC brake systems. With the aid of the coupling according to the invention of said radial piston pump to a motor/pump unit, brake systems may easily be fitted or retrofitted with a second pressure source.
An advantageous design provides that the stator and at least one portion of the rotor directed towards the stator define an electromagnetic region, at least the pump defines a hydraulic region, and at least one sealing element is provided, which separates the electromagnetic region from the hydraulic region in a fluid-tight manner. The sealing element separates the stator and the portion of the rotor facing it from the hydraulic region of the pump, in which brake fluid is situated. As a result, no brake fluid may pass into the gap between stator and rotor. No fluid frictional resistance therefore arises in the gap and the dynamic response of the electric motor is considerably improved. Said measure also increases the efficiency of the electric motor. A control-optimized combination of electric motor and pump is created. What is more, as the electromagnetic region is separated from the hydraulic region in a fluid-tight manner, no dirt may pass into the electromagnetic region. Fouling and damaging of the stator, e.g. by aggressive brake fluid, is therefore reliably prevented.
The vehicle brake system is advantageously developed in such a way that only an air gap is situated between the stator and the rotor. In the case of the vehicle brake actuator described in U.S. Pat. No. 4,435,021 A, the entire rotor is situated in the hydraulic region. The motor winding is therefore internally surrounded by a partition, which separates it from the hydraulic region and also from the rotor. In the case of the solution according to the invention, on the other hand, it is possible to dispense with said partition. The distance between the stator and the rotor may therefore be made very small. The electric motor consequently has an additionally increased efficiency and further improved response and starting characteristics.
An advantageous development provides that the stator is provided in a stationary manner in a housing, and the sealing element is formed in an annular manner between the rotor and the housing. This particularly simple construction of the invention makes it possible to use, as a sealing element, a conventional, inexpensive sealing ring, which may be selected from a wide range and may therefore be adapted extremely well to the sealing problem to be solved.
In an advantageously developed vehicle brake system, the rotor is supported rotatably about an axis of rotation in the housing by means of two bearings, which are disposed at the axial end regions of the rotor. The bearings enable precise guidance of the rotor, wherein the position of the latter may be adjusted independently of the pump.
The rotor is advantageously of a substantially cup-shaped design and comprises at its base a coaxially provided and motionally coupled drive shaft for driving the pump and the aggregate. Because the cup shape is open only in one direction, given such a design in the rotor a closed chamber for the pump may be sealed particularly easily. For example, for this purpose a sealing element may be disposed at the opening of the cup-shaped rotor.
Advantageously, however, the housing comprises a substantially hollow-cylindrical housing portion, which projects radially at the inside and coaxially into the cup-shaped rotor, and the sealing element is disposed between the hollow-cylindrical housing portion and the drive shaft. The rotor is consequently sealed at a relatively small surface and a sealing element with a small diameter may be used. Such sealing elements present a lower frictional resistance and take up only a little installation space. Furthermore, because the housing portion is disposed between the rotor and the pump, no flow-generated friction arises between rotor and pump.
The pump advantageously takes the form of a gear pump, nutating disk pump or swash-plate pump. Such a pump has a constant drive power over time and may therefore be driven by a relatively low-power electric motor.